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A Guide To Its Present And Past
Compiled and Written by the Federal Writers' Project of the Works Progress Administration for the State of New Jersey
American Guide Series

Originally published in 1939
Some of this information may no longer be current and in that case is presented for historical interest only.

Edited by GET NJ, COPYRIGHT 2002

Geology and Paleontology

Geologists divide New Jersey as it is today into three provinces. The first, known as the Appalachian Highlands Province, contains the highest ground in the State and extends northwest from a line connecting Suffern, Morristown, and Milford. Extending 20 miles south of the Ramapos to US 1 (the Newark to Trenton highway) and lying between the Delaware and Hudson Rivers, is the Triassic Lowland, a less elevated section. South of US 1 is the lowest land in the State, comprising the Coastal Plain Province.

Each section has been shaped by the interplay of sub-crustal forces and external agencies such as erosion by surface water and invading ice. And the character of each has exercised physical control over man's cultural history within its boundaries. Cities, farms, and factories are placed today largely where the results of geological processes -- not man -- suggested.

The Appalachian mountain ridge, on the northwestern boundary, resulted from tilted-up layers of hard rock that have withstood erosion while the less durable rocks were gradually worn away to form the Kittatinny Valley. The lower Highlands ridges are largely composed of hard rocks of granite, gneiss, limestone, slate, sandstone, and siliceous conglomerates. These rocks are the oldest in the State, consisting largely of pre-Cambrian and Paleozoic types. Along the Ramapo Mountains on the southern border of this region is a great fault, or fracture, dating back many millions of years to the time when a vast block of rock-crust broke away and settled. Although the hard sandstone, ridges carry a soil sufficiently hospitable for forest growth, the only productive soil is found on the soft shales and limestones of the well-settled valleys.

The Triassic Lowland, a long strip barely 20 miles wide, is the urban and industrial center of New Jersey. The underlying rocks of this section are chiefly red sandstones and shales, which through decay have given their color to the soil. Although not conducive to extensive farming, this formation has provided excellent sandstone for building and road-making.

Several ridges in this province, notably the Watchung Mountains, have successfully resisted erosion because of their hard volcanic rock. The Watchungs may owe their origin to one of New Jersey's geologic oddities, Snake Hill, which is probably the eroded stump of an ancient volcano. This rough rock-pile has a lonely site in the Hackensack meadows, just north of the Pennsylvania Railroad main line, where it is one of the first things seen by outbound travelers from New York as the train leaves the Hudson tunnel.

The most spectacular sight in this area is, of course, the Palisades of the Hudson. Rising in places to more than 500 feet, these great stone columns are the edge of what was once a thick sheet of molten rock that, forced upward from great depths in the earth's interior, spread out horizontally between layers of sedimentary sandstone and red shale-like the chocolate filling in a layer cake. Cooling slowly far beneath the surface, this layer acquired its perpendicular columns through shrinkage and cracking. Over a long period of time, erosion removed several thousand feet of sediment in the layer above, finally exposing the Palisades. Because of greater hardness they have survived countless centuries of erosion.

For 17 miles within the State this rock wall parallels the Hudson, disappearing from sight near Weehawken. But the formation can be traced under the waters of Kill van Kull to Staten Island, where it makes a farewell appearance as an unimposing little heap of rocks in an open field. Soundings have shown that the canyon of the Hudson extends 400 miles to sea -- a natural marvel easily comparable with the Grand Canyon of the Colorado.

The broad Coastal Plain region is the center of New Jersey's market gardens, pine forests, and beach playgrounds. Along the Atlantic coast south of Point Pleasant, a long broken row of sand ridges rises above sea level. These ridges have been built up offshore by the action of waves and ocean currents. Similarly, tidal marshes and beaches extend around the State from Raritan Bay on the east coast to Camden on the western boundary.

Fertile soils are found upon the inner coastal plain. An inner belt of Cretaceous greensands and marls, valuable as fertilizer, extends across the State from the Raritan to the Delaware. As a whole, the area is one of sedimentary rocks. Contrasting with the fertility of the farming district is the great pine forest that covers more than 3,000 square miles in the southeast.

Age of Invertebrates Tests involving radioactive minerals indicate that crystalline rocks in the Highlands region are at least one billion years old. Geologists have pieced together a story of New Jersey that antedates the dinosaur by many millions of years. At the earliest time in geological records, the northwestern section of the State was the floor of a long and narrow inland sea. This gulf was separated from the open Atlantic by a mountainous barrier on the site of the present continental shelf. Erosion gradually wore down the mountains, the soil and debris being distributed on the floor of the sea. Ultimately this sediment converted an arm of the sea into dry land.

The animals of this inland sea were all invertebrates; shellfish and trilobites were dominant. The shellfish superficially resembled those of our present sea, while the trilobites were peculiar animals, smaller but otherwise not unlike the king crab or horseshoe crab of the New Jersey coast today. Fossils of these animals are occasionally found in quartzite and limestone which in the form of sand and limey ooze formed the sea-floor during this period. Perfect trilobites are very rare in New Jersey. Quarries near Blairstown and Columbia have yielded fragments.

During the Ordovician period, which followed the Cambrian, limestones and shales were being deposited. The animals of the Ordovician sea were more numerous than those of the Cambrian, but again they were all spineless. Sponges, corals, shellfish, and trilobites are occasionally found in the rocks deposited in this sea, for instance near Jacksonburg, Newton, and Branchville.

Age of Reptiles. Millions of years later, during the Triassic period, came the Appalachian revolution, when the earth's crust shivered and made mountains. The eroded mountains near the sea were pushed bodily northwest, wrinkling the layers of sediment that had filled this ancient trough. These huge wrinkles were the ancestral Appalachian Mountains. A long period of erosion followed; the newly formed mountains were slowly worn down, their waste being spread upon an eastern piedmont that lay, in Triassic time, between the new mountains and the relics of the old barrier. The weight of these new deposits was t00 much for the earth's crust. A large block split off and sank, squeezing upward enormous quantities of black lava that spread over the floor of this valley. (The line of fracture is known today as the Ramapo fault.)

The elevation of the Appalachian Mountains left a valley between them and the older mountains of Appalachia. Several freshwater lakes must have existed in this valley, for today there are remains of many fish in the deposits that eventually filled the lakes. A great many of these fossil fish have been found in the vicinity of Boonton.

More sediment from the bordering mountains on the east and west covered the lava. Finally, earth movements tilted the entire strata to a gentle northwestward slope; a series of fractures enabled the crustal blocks to slip downward as they became tilted.

The irresistible forces of erosion-forces that have carved New Jersey as the State exists today, continued their assault on the mountains. The ancestral Appalachians were slowly leveled off. Another series of sediments, now known as the Cretaceous, was built up along the coast, spreading inland over part of the Triassic rocks. This encroaching sea deposited beds of gravel, sand, clay, and greensand marl that are important units of the Coastal Plain today. Ancestors of the modern shellfish inhabited these waters and built great shell beds covering many square miles; dinosaurs waded in the coastal marshes, leaving footprints on the muds of geologic time; sea serpents, sharks, crocodiles, and huge turtles disported nearby. Their habitat was probably the dense vegetation or marshes near the sea. Great forests of palmlike trees grew along the shores of these estuaries, and tangles of huge ferns and slender branchless trees, not unlike our present horse-tail rushes, choked the marshes. The finding of a fossil cycad at Woodbridge has suggested that the climate was much warmer than it is today.

The dinosaurs and some of the other reptiles of this period were numerous, and their remains have occasionally been found in southern New Jersey. A model of the large dinosaur (Hadrasaurus) found many years ago near Haddonfield can be seen in the State Museum at Trenton. Shark teeth and bones of crocodiles and turtles are often found in deposits of Cretaceous age.

During construction of the George Washington Memorial Bridge, excavations made in Triassic rock of the Palisades revealed tracks of dinosaurs. Traces and skeletons of dinosaurs and other fossil animals have been uncovered also at Fort Lee and near Princeton. Cretaceous marine fossils deposited by the sea that covered most of southern New Jersey are even more numerous than the terrestrial ones. The shells of large clams and snails and the pens of a squidlike animal (belemnite) are often found in the Cretaceous deposits at such places as New Egypt, Marlton, Crosswicks, Mullica Hill, and Lenola.

Age of Mammals. Once more the earth's crust moved. This time, however, it was not a convulsion, but a rather gentle upward push that elevated the whole Atlantic coastal belt. Streams etched out new valleys, with the hardest rock surfaces resisting erosion longest. The Delaware River came to grips with the ancient bulk of Kittatinny Mountains -- a grand-father in a range of patriarchs. Whereas the eroded remains of Kittatinny once stood scarcely higher than the river's crest, its hard rock was now rising anew as part of the general onward and upward movement. But the mountain's uplift was slow enough to give the river a chance to use its cutting tools. The Delaware did not need to carve through a mountain wall, nor did it find a ready-made gap. It merely held its course as the mountain rose, sawing downward through both hard and soft rock. The result of that successful operation is the Delaware Water Gap.

Most of the ancient plane surfaces disappeared at this time, except for the table top of the Palisades and the flat summits of venerable Schooley's and Kittatinny Mountains. The Schooley peneplane, as it is designated by geologists, is a conspicuous but little known souvenir of a long stage in erosional history.

It was at the beginning of this period, the Tertiary, that the dinosaurs and other large reptiles suddenly and rather mysteriously disappeared. Their place was taken by the mammals. Although many kinds of mammals were living throughout the country during this period, and New Jersey probably had its quota, Tertiary fossils are not common.

The northern part of New Jersey was much as it is today, while the southern part was covered several times by a warm shallow sea. Many of the shellfish were similar to those of the Cretaceous seas, but others were more like those of our present oceans. There are various deposits of Tertiary fossils in New Jersey, but probably the best known is near Shiloh in Cumberland County, where a large fauna of Miocene fossils has been found in the marl pits.

The Ice Age. The surface of New Jersey was geologically ready for man something less than a million years ago. Then the climate gradually became colder. Down the valleys of Lake Champlain, the Connecticut and St. Lawrence Rivers, long fingers of ice from Canada crept southward. Finally these fingers merged into a solid sheet of ice that swept all resistance before it.

Vast quantities of rock, soil, and debris were pushed across country for many miles. Remnants of this material, known as the terminal moraine, still mark the former edge of the ice from Perth Amboy northward through Plainfield, Summit, and Madison to Denville; and from Denville due west through Netcong, Hackettstown, and Belvidere to the Delaware River. A line through these towns marks the southern limit of the glacier's advance.

Mammoths and mastodons roamed the country at this time. One of the finest specimens of mastodon found in the State is in the museum of Rutgers University. The skeleton, remarkably complete, was excavated in 1869 from a bed of gray marl in Mannington Township, Salem County. It is 22 feet long and 9 feet 8 inches high. Six other mastodon skeletons were found between Vienna and Hackettstown, and several teeth were recently dredged off the coast.

Although this period, the Quaternary or Pleistocene, is called the Ice Age, there were periods between advances of the ice when the climate was probably milder than today. Water from melted ice flooded much of the land adjoining the present shore line. Fossils from this warm, interglacial sea include species that are now restricted to warmer waters off the Carolinas and Florida. Many specimens were recently found when sand was pumped from the bottom of the marshes in Cape May and Atlantic Counties to convert the lowlands into real estate developments. In addition to shells, a few larger fossils were found, including bones of the deer, whale, and numerous fishes.

Drainage systems were, of course, seriously disturbed by the arrival of the glacier, by the newly formed deposits, and by the great amounts of water released when the ice melted. Many of the lakes and swamps of Sussex County are of glacial origin. The Passaic River, which formerly pursued a short route seaward through the Watchung Mountains at Summit, was blocked by morainal material. A large lake was formed behind the mountains and temporarily overflowed near Bernardsville. As the ice edge receded, perhaps no longer than 20,000 years ago, the river found lower outlets for this Lake Passaic, finally adopting a hairpin course through Paterson -- a 20 -- mile detour. The river is still making that detour today, the change being responsible for the spectacular Passaic Falls within the city of Paterson. The last of Lake Passaic may be seen in the Great Swamp near Myersville in Morris County.

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